People who have already seen something know they've seen it. They can just skip it. To somebody else it will be new. The vast majority of items being called reposts on reddit were things I had never seen. Whining about reposts might give someone a false sense of accomplishment, but I found it to be useless noise.
That's not a terrible idea - it would be a link to the existing discussion of the topic, which is informative. I like that better than people just whining RePoSt!!1!
My thoughts exactly. On reddit I used to reply to repost complaints, which I find annoying, by saying that they were the most reposted thing I saw. But tbh their frequency has seemed to decrease, almost as if they're being auto-removed. If so, I appreciate it. A subject showing up repeatedly just means somebody's still interested in it.